1. Field of the Invention
The invention relates generally to electrical relays and more specifically to integrated solid state relays that are network controlled and therefore have network addresses.
2. Description of the Prior Art
Relays are universally used to control one load in response to one control line. The vast majority of relays are simple, unintelligent devices that simply conduct load current when an input voltage is above some switch threshold. Traditional relays were electromechanical devices in which a solenoid was used to pull-in a set of switch contacts. More recently, solid-state semiconductor devices have been used in so-called xe2x80x9csolid-state relaysxe2x80x9d (SSRs). Input to output circuit isolation has been widely achieved through the use of opto-isolators, e.g., combinations of light emitting diodes (LEDs) and photodetectors. Power MOSFETs, SCRs and TRIACs are very common in the output circuits of such SSRs.
The industrial uses of relays typically involve the switching of high currents, voltages, or powers very near the load itself. This permits relatively light wiring to be run to a controller because the currents, voltages, or powers needed to drive the relay are orders of magnitude less than those of the loads. Even so, such control circuit wiring is limited in how far the controller can be removed from the loads it controls. In modern industrial control applications, the number of control circuits and loads can run into the hundreds. The wiring and the dedicated channels to control hundreds of relays can quickly become impractical and very expensive.
Recently, computers have revolutionized the way control systems are designed and implemented. Micro-controllers, programmable logic controllers (PLCs) and other programmable devices have become ubiquitous in industrial automation. Several manufacturers now offer products with network controlled components. These typically communicate through a network, rather than use traditional hard-wired point-to-point connections between each device and the controller.
As industrial networks have grown in popularity, combining devices from different manufacturers has become a problem because different proprietary communications interfaces and protocols have been used. Such incompatibilities have resulted in various industry-standard topologies and protocols being adopted, e.g., so-called RS-232, RS-485, Fieldbus, PROFIBUS, Seriplex, SDS, DeviceNet and CAN. It is widely believed that strict adherence to industry standards promotes multi-vendor connectivity, such that devices from different manufacturers will automatically work together in the same network.
Even though there is a wide variety of intelligent relay and control devices being marketed, there is no general purpose solid state relay available that combines the intelligence of these protocols with the functionality and versatility of a high capacity relay.
In control systems, relays are used to turn on motors, valves, lights, etc. In prior art systems such relays are driven by a PLC, measurement sensor, parallel output port of a computer, etc. Although this may work fine for applications in which the number of outputs is not a limitation, and where the relays are located physically close to their controller, in others this is less acceptable as the amount of wiring and or multiplexers or multi-controllers becomes prohibitive.
It is therefore an object of the present invention to provide a general purpose solid state relay compatible with standard industrial networks.
It is another object of the present invention to provide a solid-state relay that permits wider control from more centralized supervisory centers.
Briefly, an addressable process control relay embodiment of the present invention comprises a solid-state relay with an embedded network client. Such client is basically hardware compatible with the physical layer interfaces of a general class of serial networks, and has a variety of down-loadable or embedded protocol personalities that can respond to a particular proprietary network. Such protocol personalities are preferred to include: Fieldbus, process field bus (PROFIBUS), Seriplex, smart distributed system (SDS), DeviceNet, controller area network (CAN), etc.
An advantage of the present invention is that an addressable solid-state relay is provided that eliminates the need for otherwise redundant I/O modules, cards, and single-personality addressable relays.
Another advantage of the present invention is that an addressable solid-state relay is provided that simplifies the installation and maintenance of industrial process control systems.
These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in the various drawing figures.